The cited patent applications teach high capacity digital watermarks that can be completely removed, restoring a watermarked content object (e.g., an image) to its original, pristine state. (See also Tian, “Wavelet-Based Reversible Watermarking for Authentication,” Proc. of SPIE, Vol. 4675, pp. 679-690, January 2002; and Tian, “Reversible Watermarking by Difference Expansion,” Proc. Multimedia Security Workshop, Dec. 6, 2002.)
Other reversible watermarking techniques are also known, e.g., in U.S. Pat. Nos. 5,646,997 and 6,278,791, and in Fridrich et al, “Lossless Data Embedding for All Image Formats,” Proc. SPIE, Vol. 4675, pp. 572-583, January 2002; Dittmann et al, “Watermarking Protocols For Authentication And Ownership Protection Based On Timestamps And Holograms,” Proc. SPIE, Vol. 4675, pp. 240-251, January, 2002; Fridrich et al, “Invertible Authentication,” Proc. SPIE, Vol. 4314, pp. 197-208, January, 2001; Macq, “Lossless Multiresolution Transform For Image Authenticating Watermarking,” Proceedings of EUSIPCO, September 2000; Vleeschouwer et al, “Circular Interpretation Of Histogram For Reversible Watermarking,” Proceedings of IEEE 4th Workshop on Multimedia Signal Processing, October 2001; Kalker et al, “Capacity bounds And Constructions For Reversible Data Hiding,” Proceedings of the 14th International Conference on Digital Signal Processing, volume 1, pages 71-76, July 2002; and Celik et al, “Reversible Data Hiding,” Proceedings of International Conference on Image Processing,volume II, pages 157-160, September 2002. Other reversible watermarking techniques will doubtless be developed in the future.
The ability to remove a watermark from an encoded image opens the possibility of various novel applications. Several such applications are detailed herein.
One application employs a reversible (frail) watermark in conjunction with a second (robust) watermark. The payload of the reversible watermark conveys information about the robust watermark (e.g., encoding parameters, or an error signal), permitting removal of the robust watermark from an uncorrupted encoded image. By such arrangements, the encoded image can be fully restored to its pristine, unencoded state even if several different watermarks have been applied.
In a related application, the information about the robust watermark can be stored in a memory, and accessed through linking data encoded in one of the watermarks.
In all such arrangements, after the watermarks have been removed, an image hash can be computed and checked against a hash made prior to any watermarking, to confirm perfect restoration of the image to its original state. (The latter hash can be conveyed with the image via one of the watermarks, or it can be stored in a memory and accessed through linking data encoded in one of the watermarks.)
Another application permits different classes of consumers to gain access to different versions of an image. A pristine image is intentionally degraded in some fashion, and distributed to consumers. By reference to one or more watermarks in the degraded image, some or all of the degradation can be removed, or transformed to a less-objectionable state. (The degradation may be that introduced by watermark encoding, or of another form.) Through such arrangements, image consumers with different authorization rights can gain access to versions of the image having differing qualities.
Various combinations of the foregoing and other arrangements are also contemplated.
These and other features and advantages enabled by the present invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.